1. Field of the Invention
The invention relates to a portable automated pipette. More particularly, the invention provides a portable automated pipette having a step motor with feedback function.
2. Description of the Related Art
A pipette is a device that, like a syringe, picks up or dispenses a predetermined volume of liquid by a pumping means. The pumping means includes a motor transmission mechanism that can linearly move, and an aspirator removing mechanism. The pumping means is usually associated with a control circuit to control one or more aspirators. For example, the U.S. Pat. No. 4,671,123, U.S. Pat. No. 4,905,526, and U.S. Pat. No. 6,254,832, which are incorporated by reference herein, disclose pipettes that pick up or dispense a constant volume of liquid.
However, it is difficult to accurately keep a rotational speed of the motor transmission mechanism constant due to the manual operation or the liquid viscosity. For example, picking up 1 μl of liquid normally needs 100 revolutions of the motor. If a problem of manual operational occurs, the motor only runs, for example, 98 revolutions, which can not meet the requirement of accurate liquid picking. Furthermore, the pipette is incapable of detecting whether an aspirator is removed.